This study evaluated the relationship between low-level phosgene (COCl2) exposure and pulmonary change or damage. Male Sprague-Dawley rats were exposed to phosgene for 4 hr at concentrations of 0.125 to 1.0 ppm (30, 60, 120, and 240 ppm X min). We examined the dose-related changes in body weight, lung wet and dry weights, lavage fluid protein concentrations (LFP), total cell count, and cell differential in rats exposed to phosgene under carefully controlled conditions. These parameters were measured at the conclusion of single acute exposures and for 3 days postexposure. Significant changes in lung weights (wet and dry) were observed following exposure to 120 and 240 ppm X min phosgene and the LFP was significantly altered at 60 ppm X min. The changes in lung wet and dry weights pooled over all times and phosgene concentrations each correlated significantly with the change in LFP induced by phosgene. The total number of cells in the lavage fluid of phosgene-exposed rats was increased, and the most sensitive cellular indicator of phosgene inhalation was the increase in the percentage of polymorphonuclear leukocytes (PMNs). These results confirm that LFP concentration and cellular differentials can be used as an index of lung damage due to phosgene. A dose-response relationship for the measured parameters was observed. Over the dosage range studied, the return of all measured parameters to near control levels within 3 days following exposure showed that the pulmonary damage was reversible or rapidly reparable. Although the acute effects were shown to be reversible, studies on chronic, low-level phosgene exposures are necessary to determine safe levels for industrial employees.